Electronic article surveillance systems have been used for many years as a means of deterring retail shoplifting in clothing stores, electronic stores, and a myriad of other retail establishments. Generally speaking, an EAS system will begin with a tag, consisting of a durable and reliable, yet small, sensor tag which is affixed to the article to be detected in such a way that it cannot be easily removed by a customer in the store. Usually, the system depends upon the feature that the attachment mechanism is constructed such that it can only be removed by the use of a specialized tool which is only in the possession of an authorized store personnel at the checkout register or exit port for the establishment. In the event that an EAS tag is not removed from a protected article prior to exiting the store, an alarm or other signal is activated.
In many commercially available EAS systems, one or more antennas are placed at the exits and entrances to the retail location. These antennas set up zones, sometimes referred to as interrogation zones, in which an EAS tag (or marker) may be sensed. At least one antenna serves the function of sending out what is called an interrogation signal. The markers on the merchandise are affected by this signal and will respond with a signal of their own. Either the same antenna that sends out the interrogation signal or other additional antennas can sense the signals from the markers. The most effective way to do this is by stopping the broadcast of the interrogation signal to listen for the signals emanating from the markers. If a marker is sensed within the zone created by the antennas, it is presumed that an article is being removed without purchase, and alarms are set off. These alarms may be audible alarms for general broadcast or the alarms may be silent alarms in the form of a light at a check-out counter or security station, etc. Additionally, some EAS tags have onboard audible alarm generators and can generate audible alarms by themselves. These tags may produce this audible alarm when onboard logic elements determine that the tag being removed from the store, or when the larger EAS system communicates to the tag to alarm. The onboard logic elements and the larger EAS system may also cause the tag to cease to alarm under certain situations.
In order to make an EAS system effective, one must consider how to make the EAS tags tamper resistant. This is an on-going effort, because over time, thieves become more capable in learning how to defeat an EAS tag. The retailer (and the tag manufacturer) must consider how to detect and prevent tampering with the tags. The particular construction of a tag will determine how tampering is detected.
An assortment of attachment mechanisms are available in the prior art. One of the more common and more successful attachment mechanisms is an EAS hard tag, consisting of a tack which is used to physically pin the EAS tag base to the protected article. The tag base is usually constructed of a hard and durable plastic and is generally in the neighborhood of three inches long. The tag serves as a housing for an electronic signal generation means secured within the housing, and which is designed to be immune to tampering. A cap on the tack keeps the tag attached to the article.
Another common and successful method of attaching tags, or transponders, is a lanyard. One end of the lanyard is fixed in the transponder and the other end is capable of being inserted into an aperture in the transponder where it can be retained by the transponder. The lanyard can pass through an aperture on the article to be protected or may be placed around an article in a position where it cannot be simply slid off the article. The lanyard is typically constructed of material that is very difficult to break or cut, but yet, is easy to bend into place. A variation on lanyard tags passes the unfixed end of the lanyard through the body of its tag to form a loop which may be adjusted onto an object by pulling the unfixed end. A clutch in the body prevents the lanyard loop from being enlarged unless the clutch is release by an authorized person. Some tags may form more than one loop.
A common device for releasably retaining both tack shafts and lanyards is a ball clutch mechanism. The ball clutch mechanism may be constructed to release the retained item after application of a magnetic force to the tag. Other clips and clamps may also be used. Other types of tags may employ vials of ink, which may break if the tag is physically bent, thereby destroying the benefit of the theft attempt.
While tack, lanyard, and other types of tags have found wide use in protecting objects, they must remain attached to a given object to protect it. A common manner of defeating an EAS tag is to forcibly remove the tag from the object being protected. A countermeasure employed with some EAS tags is the introduction of a switch which has its state changed and arms the tag when a tag is attached to an object to be protected. This switch is often termed a plunger switch. The actuated part of the switch is a small plunger that extends from the tag at location where the object and tag interact. For example, in tags employing a tack, a switch is positioned on the tag at a location beneath the head of the tack. When the tack is inserted through an object, the object and the head of the tack bear upon the switch and change its state.
Associated devices may communicate with electronics within the EAS tag to add an additional step to the tag arming process. When the tag is attached to an object and the state of the switch changed, this change of state functions as confirmation that the tag is attached, and an authorized person can use an associated device to wirelessly communicate with the tag to complete the tag installation and arming process. Once armed, if a tag is forcibly removed, the switch's state again changes, and the electronics of the EAS tag determine that an alarm condition exists. The EAS tag can sound an audible alarm with an onboard audible alarm generator or wirelessly communicate an alarm to other elements of the EAS system.
Although the presence of a plunger switch can aid the ability to detect when a tag is attached to an object, the switch may not operate consistently. For example, if a tag is attached to an article of clothing, the plunger of the switch may merely protrude into the clothing and the state of the switch may not change. Alternatively, the tag may install properly, but with handling of the clothing, the plunger may move and change the state of the switch, causing a false alarm; a very undesirable occurrence. In other situations, the objects may be too irregularly shaped to guarantee contact with the plunger. If a recess in an irregularly shaped object coincides with the location of the switch, the switch will not detect the presence of the object, and the tag will fail to arm. Alternatively, a tag may be successfully attached to an irregular object and armed, but a small shift of the object may release the switch, which would cause the undesired false alarm. Embodiments of the present invention can work with the several prior art embodiments of EAS tags employing plunger switches to counter the deficiencies discussed above.